Measured and Simulated Runoff to the Lower Charles River, Massachusetts, October
1999September 2000

U.S. Geological Survey Water-Resources Investigations Report
02-4129

By P.J. Zarriello and L.K. Barlow

ABSTRACT

The lower Charles River, the water body between the Watertown Dam and the New
Charles River Dam, is an important recreational resource for the Boston, Massachusetts,
metropolitan area, but impaired water quality has affected its use. The goal
of making this resource fishable and swimmable requires a better understanding
of combined-sewer-overflow discharges, non-combined-sewer-overflow stormwater
runoff, and constituent loads. This report documents the modeling effort used
to calculate non-combined-sewer-overflow runoff to the lower Charles River.

During the 2000 water year, October 1, 1999September 30, 2000, the U.S.
Geological Survey collected precipitation data at Watertown Dam and compiled
data from five other precipitation gages in or near the watershed. In addition,
surface-water discharge data were collected at eight sitesthree relatively
homogenous land-use sites, four major tributary sites, and the Charles River
at Watertown Dam, which is the divide between the upper and lower watersheds.
The precipitation and discharge data were used to run and calibrate Stormwater
Management Models developed for the three land-use subbasins (single-family,
multi-family, and commercial), and the two tributary subbasins (Laundry and
Faneuil Brooks). These calibrated models were used to develop a sixth model
to simulate 54 ungaged outfalls to the lower Charles River. Models developed
by the U.S. Geological Survey at gaged sites were calibrated with up to 24 storms.
Each model was evaluated by comparing simulated discharge against measured discharge
for all storms with appreciable precipitation and reliable discharge data. The
model-fit statistics indicated that the models generally were well calibrated
to peak discharge and runoff volumes. The model fit of the commercial land-use
subbasin was not as well calibrated compared to the other models because the
measured flows appear to be affected by variable conditions not represented
in the model. A separate Stormwater Management Model of the Stony Brook Subbasin
previously developed by others was evaluated with the newly collected data from
this study; this model had a model fit comparable to the models developed by
the U.S. Geological Survey.

The total annual runoff to the lower Charles River during the 2000 water year,
not including contributions from combined-sewer-overflows except from the Stony
Brook Subbasin, was 16,500 million cubic feet; 92 percent of the inflow was
from the Charles River above Watertown Dam, 3 percent was from the Stony Brook
Subbasin, 2 percent was from the Muddy River Subbasin, and less than 1 percent
was from the combined inflows of Laundry and Faneuil Brooks. The remaining ungaged
drainage area contributed about 2 percent of the total annual inflow to the
lower Charles River. Excluding discharge from the Charles River above Watertown
Dam, total annual runoff to the lower Charles River was 1,240 million cubic
feet; 39 percent was from the Stony Brook Subbasin, 27 percent was from the
Muddy River, which includes runoff that drains to the Muddy River conduit, 7
percent was from the Laundry Brook Subbasin, and 4 percent was from the Faneuil
Brook Subbasin. Flow from the ungaged areas composed about 23 percent of the
total annual inflow to the lower Charles River, excluding discharge from the
Charles River above Watertown Dam.

Runoff to the lower Charles River was calculated for two design storms representing
a 3-month and a 1-year event, 1.84 and 2.79 inches of total rainfall, respectively.
These simulated discharges were provided to the Massachusetts Water Resources
Authority for use in a receiving-water model of the lower Charles River. Total
storm runoff to the lower Charles River was 111 and 257 million cubic feet for
the 3-month and 1-year storms, respectively. Excluding discharge from the Charles
River above Watertown Dam, total runoff to the lower Charles River was 30 and
53 million cubic feet for the 3-month and 1-year storms, respectively. Runoff
from the various tributary areas for the design storms was about in the same
proportion as that for the annual runoff.

CONTENTS

Abstract

Introduction

Purpose and Scope

Description of the Lower Charles River and its Watershed

Climate

Land Use

Soils

Topography

Hydrology

Previous Investigations

Acknowledgments

Gaged Subbasins

Discharge

Charles River at Watertown Station01104615

Single-Family Land-Use Station01104630

Laundry Brook Station01104640

Faneuil Brook Station01104660

Multifamily Land-Use Station01104673

Commercial Land-Use Station01104677

Muddy River Station01104683

Stony Brook Station01104687

Data Management

Precipitation-Runoff Model

Functional Description of SWMM

Model Development

Data

Spatial Data

Time-Series Data

Representation of Overland Runoff

Assignment of Subcatchments to Precipitation Gages

Subcatchment Parameterization

Representation of the Drainage Network

Drainage Network Parameterization

Pond Storage

Model Calibration

Model Fit

Land-Use Subbasin Models

Single-Family Residential

Multifamily Residential

Commercial

Tributary Subbasin Models

Laundry Brook

Faneuil Brook

Stony Brook

Relative Model Fit

Design Storms

Sensitivity Analysis

Model Limitations

Runoff to the Lower Charles River

Annual and Monthly Water Budget

Single-Family Land-use Subbasin

Multifamily Land-Use Subbasin

Commercial Land-Use Subbasin

Laundry Brook Subbasin

Faneuil Brook Subbasin

Stony Brook Subbasin

Total inflows to the Lower Charles River

Design Storms

Summary

References Cited

Appendix 1A-G: Model Areas and Schematics of the StormWater
Management Model (SWMM) Elements used to Represent the Model Areas

Appendix 2: Rainfall Characteristics of Storms at BWSC-CS4,
Lower Charles River Watershed, 2000 water year